It is conventional in stationary telephones installed at homes or offices for common use or personal use that any one can use them with no difficulty so long as he/she knows how to use them.
Now, in recent years, stationary telephones are adding various functions other than oral communication function, thereby handling various kinds of data by such telephones.
However, unlike cellular phones that are always carried with their holders, it is possible that the data stored in stationary telephones are leaked to ill willed unidentified persons, especially when the owners of the stationary telephones are absent from their telephones. It is also possible that the telephones are used by someone else without owners' permission.
In order to prevent use by unauthorized person, proposed are telephone sets provided with a security function that restricts operation of such telephones as disclosed in Japanese patent publication no. 11-8743 (JP-A-99-8743) entitled “Communication Terminal” (referred to as the Patent Document 1 below).
However, conventional technologies such as disclosed in the Patent Document 1 have the following problems or drawbacks. That is, setup procedures of the stationary telephones are complicated. They require a plurality of operations and frequent changes of the settings are not easy. As a result, it is typical for most of the users to use such telephones without changing from the initial settings. This means that the user tends to leave the telephone with the initial settings, i.e., without activating the complicated security settings when he/she needs to temporarily leave his/her seat for a short time break or meeting.